Question 2
What is the solubility of a substance?
The right answer is the one marked above.
The maximum mass of solute that dissolves in 100 g of solvent at a given temperature. Fixing the mass of solvent and the temperature is what makes two solutes comparable at all.
The word maximum is doing work: the solution must be saturated. How fast a solute dissolves is a different question entirely and has nothing to do with solubility.